Lois McMaster Bujold has won as many Hugo awards as Robert Heinlein and she is still going strong. Normally working in the Sci-Fi category, she writes a some fantasy novels (Curse of Chalion) that get a lot of critical acclaim, and one even wins a Nebula award. Yet, I'm pretty sure R.A. Salvatore Drizzt books outsell her books by a wide margin.
Publishers are going to buy stories that they can market and get good sales. Authors and publishers instrested in the fantasy market don't have a whole lot of incentive to break from the norm. In Chalion, the main character is a middle aged man who has been through hell so his view on life is a bit more subdued. Breaking the mold and taking some risks can bankrupt an author in real life if the sales tank. Most authors don't make that much money and to take a year or two to write a novel that isn't going to put money in the bank isn't going to be an appealing option.
